Incidence of pulmonary and venous thromboembolism in pregnancies after in vitro fertilisation: cross sectional study

Since the birth of the first “test tube baby” in 1978, in vitro fertilisation has been used increasingly to assist reproduction. To date about five million people have been born after in vitro fertilisation and this method is regarded as an effective and safe technique, with about a third of attempts resulting in pregnancy and a quarter in live births.

It is well known that the risk of venous thromboembolism is increased during normal pregnancy. According to data from Sweden and Norway during the early 1990s venous thromboembolism occurred in slightly more than one out of 1000 pregnant women.Venous thromboembolism in pregnant women after in vitro fertilisation has been reported in numerous case reports and in two small consecutive series, two out of 2500 (0.8/1000) women and three out of 2748 (1.1/1000) women. Notably, these estimates of incidence have been claimed to be comparable to those during natural pregnancy. A recent report suggested that the incidence of venous thromboembolism after in vitro fertilisation was substantially increased during the first trimester but not in the other two trimesters. No information exists on the risk of pulmonary embolism after in vitro fertilisation, which is important because embolism is a leading cause of maternal mortality. Moreover, in the recently published report outpatient diagnoses were not included and no adjustments were made for the increased incidence of venous thromboembolism during the past decade. Furthermore, no adjustments were made for the reported age difference in cases and controls, making the strength of the risk estimate of a 10-fold increase during the first trimester less exact.

We compared the risk of pulmonary embolism and venous thromboembolism in pregnant women after in vitro fertilisation with that of age and time matched women with natural pregnancy.